Urology - Urolithiasis: Pathophysiology And Presentation

Question 1

Epidemiology

Answer 1

• Lifetime incidence: 15%
• M>F (3:1)
• Peak age 20-40

Question 2

Pathophysiology

Answer 2

• Increased concentration of urinary solute
• Decreased urine volume
• Urinary stasis

Question 3

Commonest anatomical sites

Answer 3

• Pelviureteric junction
• Crossing the iliac vessels at pelvic brim
• VUJ
• These three are the narrowest bits of ureters
• under vas or uterine artery

Question 4

Presentation: ureteric colic

Answer 4

• severe loin to groun pain +/- pain in scrotum or labia
• Associated with nausea/vomiting
• Pt cannot lie still (vs v still in peritonism)

Question 5

Presentation: bladder or urethral obstruction

Answer 5

• Bladder irritability: frequency, dysuria, haematuria
• strangury: painful urinary tenesmus
• suprapubic pain radiating to ether tip of penis or in labia
• pain and haematuria worse at end of micturition

Question 6

Presentation: other possible features

Answer 6

• UTI
• Haematuria
• Sterile pyuria

Question 7

Calcium oxalate stones:

• Percentage of calculi?
• Risk factors?
• Radio visible?
• Mean urine pH when these occur?

Answer 7

• 85% of stones
• Hypercalciuria: major risk factor
• Stones are radio-opaque (but less than calcium phosphate stones)
• pH = 6 - can occur under variable urine acidities

Question 7

Cystine stones

• Percentage of calculi?
• Risk factors?
• Radio visible?
• Mean urine pH when these occur?

Answer 7

• 1% of stones
• Inherited recessive disorder of transmembrane cystine transport, leads to decreased absorption of cystine and renal tubule
• Associated with Fanconi syndrome
• Occurs in conditions of normal urine acidity (eg pH = 6.5)

Question 7

Uric acid stones

• Percentage of calculi?
• Risk factors?
• Radio visible?
• Mean urine pH when these occur?

Answer 7

• 5-10%
• uric acid is a product of purine metabolism (eg found in Gout pts)
• Can be caused by disease with extensive tissue breakdown - eg malignancy
• Radiolucent
• Tend to precipitate when urine acid is low pH = 5.5

Question 8

Calcium phosphate stones

• Percentage of calculi?
• Risk factors?
• Radio visible?

Answer 8

• 10%
• May occur in renal tubular acidosis
• High urinary pH increases supersaturation of uric with calcium and phosphate
• Radio-opaque stones - composition is similar to bone

Question 9

Struvate stones

• Percentage of calculi?
• Risk factors?
• Radio visible?
• Mean urine pH when these occur?

Answer 9

• 2-20%
• Stones formed from Mg, ammonium and phosphate
• Occurs as a result of urease producing bacteria (associated with chronic infections)
• Under the alkaline conditions produced, crystals can precipitate (pH >7.2)
• Slightly radio-opaque

Question 10

How are stag horn calculi created? What infections can predispose to their formation?

Answer 10

• Involve renal pelvis and extend into at least 2 calyces
• Develop in alkaline urine and are composed of struvite (ammonium, magnesium phosphate, triple phosphate)
• Ureaplasma urealyticum and Proteus infection predispose to their formation.

Question 11

What is the imaging of choice in suspected renal colic?

Answer 11

-Non-contrast CT KUB
-Can us US to examine for hydronephrosis/hydroureter but not 1st choice for renal stones
(MRI/IV urogram not appropriate at this stage)